Investigation on Reverse Water-gas Shift over La2NiO4
Catalyst by cw-Cavity Enhanced Absorption Spectroscopy during CH4/CO2 Reforming
B.S. Liu, Ling Li, C.T. Au1, A.S.-C. Cheung Department of Chemistry, The University of Hong Kong, Pokfulam Road,
Hong Kong, China
1Department of Chemistry and Centre for Surface Analysis and Research, Hong Kong Baptist University, Kowloon Tong, Hong Kong, China
Supported by the Research Grants Council of the Hong Kong Special Administrative Region, China (Project No. HKU 7101/02P).
Background
CO2 reforming : CH4 + CO2 → 2CO +2H2
catalyst
Methane is available in huge quantity, besides burning, there are many way to utilize it .
Coupling reaction: CH4 + CH4 C2H6 + etc…
Synthesis gas
Steam reforming: CH4 + H2O → CO + 3H2 Synthesis gas
Aromatization: nCH4 C6H6 , C10H8 + …
Background
CH4 + CO2 → 2CO +2H2 cat.
Numerous studies on CH4/CO2 reforming reaction using Ni-based catalysts.
CO2 + H2 CO + H2O
Synthesis gas
Problems: (i) Low yield ( ~55%)
(ii) Carbon deposit (~after 1 hour)
Our studies:
Reverse water-gas shift (RWGS) reaction over La2NiO4
catalyst during CH4/CO2 reforming by continuous wave
cavity enhanced absorption spectroscopy (CEAS).Associated reaction:
Experimental Setup for CEAS
Experimental Conditions:
Catalyst:
Ni(NO3)2· 6 H2O + HNO3 + La2O3 ’ La2NiO4 ’ + · · ·
50 mg ‘La2NiO4 ’sol-gel-generated catalyst at >500 oC
Laser system:
Tunable diode laser: 1279-1341 nm, 5 mWLinewidth: 5 MHz
High reflective mirror: R > 0.99995
Wavenumber (cm -1)
7510.5 7510.8 7511.1 7511.4
= H2O = CH4
2000 s
1500 s
1000 s
500 s
CEA spectra of CH4 and H2O obtained at different pulsing rate (of
CH4/CO2 reaction. (Temperature = 700 oC)
Results
HITRAN Data Base
CH4 7510.59 – 7511.20
H2O 7511.30
102 1
03
1031
01
Molecule Absorption (cm-1)Vibrationaltransition Rotational
J =0 (Q branch)
J = 5, Ka = 0, Kc= 5
J = 6, Ka = 2, Kc= 4
Wavenumber (cm -1)
7510.5 7510.8 7511.1 7511.4
= H2O = CH4
2000 s
1500 s
1000 s
500 s
CEA spectra of CH4 and H2O obtained at different pulsing rate (of
CH4/CO2 reaction. (Temperature = 700 oC)
Results
CEA spectra of CH4 and H2O obtained at different time on stream.
(reaction temperature =700 oC); fixed pulsing duration
Wavenumber (cm -1)
7510.6 7510.8 7511.0 7511.2 7511.4
CH4
H2O
225 min
95 min
15 min
0 min
After long reaction time, deactivation of
catalyst
Results
(1) The conversion of CO2 over La2NiO4 catalyst was
nearly 8.0 % higher than that of methane, attributable to the contribution of RWGS reaction:
CO2 + H2 CO + H2O H = + 41 kJ/mol
(2) The H2O formation in RWGS reaction increases as the temperature of the catalyst increases because of the formation of more H2.
CH4 + CO2 → 2CO + 2H2
(More than one channel for the consumption of CO2)
High Resolution Transmission electron microscopy (HRTEM) images of as-prepared La2NiO4 sol-gel-generated catalyst
HRTEM photographs of used La2NiO4 catalyst for CH4/CO2
reforming for 5 h under the condition of supersonic jet expansion; scale (a) 200 nm (b) 5 nm.
(a) (b)
Cavity enhanced absorption spectroscopy(CEAS) is an excellent technique for monitoring catalytic reaction in situ.
The reverse water-gas shift (RWGS) reaction promoted the conversion of CO2 and decreased the partial pressure of hydrogen.
With high sensitivity, it is envisaged that chemical intermediates such as HCO, OH and CH3 radicals produced in catalytic reaction could also be detected and studied.
Conclusion and Future work
Schematic Diagram of Cavity Ring-down / Raman Shifter Experimental Setup
Cavity ring down spectrum of CH4/CO2 reforming reaction at different temperature (1573 nm).
6357.0 6357.5 6358.0 6358.5 6359.0 6359.5
CO2
CO2
CO2
CO
CO2
700 oC
600 oC
500 oC
400 oC
room temp.
Sig
na
l
Wavenumber /cm-1